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Correct answer: 17280
- Let us count the required arrangements in two separate cases:
- Case 1: All 5 boys sit together.
- Case 2: No two boys sit together.
Since these two cases cannot happen simultaneously (because if all 5 boys are together, then certainly boys are adjacent), we can add the counts directly.
- Case 1: All 5 boys sit together
Treat the 5 boys as one block.
Then we have:
- 1 block of boys
- 4 girls
So total objects to arrange = .
These can be arranged in: ways.
Within the boys' block, the 5 boys can be arranged in: ways.
Hence total arrangements in this case:
- Case 2: No two boys sit together
First arrange the 4 girls.
This can be done in: ways.
After arranging the girls, the available gaps are: So there are gaps.
To ensure no two boys sit together, we must place the 5 boys in these 5 gaps, exactly one boy in each gap.
The 5 boys can be arranged in these 5 gaps in: ways.
Thus total arrangements in this case:
- Total required arrangements
So the required number of ways is:
- Comparison with stored correct answer
Stored correct answer =
Our derived answer =
Hence, the answer agrees with the stored correct answer.
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